Grinding machine for bearing rings and method for setting tangency conditions in such a machine

ABSTRACT

A grinding machine for bearing rings includes a frame, a rotating grinding wheel rotationally movable around a first rotation axis, a working station where a bearing ring stands during a surface grinding operation, a chuck for holding a bearing ring, the chuck being rotationally movable around a second rotation axis. The machine includes a first automatic mechanism to set the position of a shaping tool with respect to an outer peripheral edge of the grinding wheel, these first automatic mechanism includes an electric motor, an encoder coupled to the electric motor to detect a rotation of an output shaft of the motor, a sensor of the position of the shaping tool along a translation axis and a comparator to compare output signals from each of the encoder and the sensor. The machine also includes second automatic mechanism to set the axial position of the chuck along the second rotation axis.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Non-Provisional Patent Application, filed under the Paris Convention, claims the benefit of European Patent (EP) Application Number 14305618.2 filed on 25 Apr. 2014 (25 Apr. 2014), which is incorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a grinding machine which can be used for grinding of bearing rings. This invention also relates to a method for setting tangency conditions between a grinding wheel of such a machine and its environment.

BACKGROUND OF THE INVENTION

In the field of bearings manufacturing, it is known, e.g. from WO-A-2008 082 140, to use a grinding machine provided with a rotating grinding wheel movable in rotation around an axis. It is known that such a grinding wheel must interact, on the one hand, with a shaping tool, in order to conform its outer peripheral edge to the actual geometry of a bearing wheel to be processed, and, on the other hand, with bearing rings successively installed within a working station of the grinding machine and held in this working station by a chuck. Because of these interactions, it is important to assess when the grinding wheel is tangent with the shaping tool and with the chuck, during setting of the grinding machine for a new type of bearing ring to be processed. Up to now the detection of the tangency positions of these elements is done manually, which requires a qualified manpower and a high level of concentration of the operator. This is time consuming and expensive.

SUMMARY OF THE INVENTION

This invention aims at solving these problems with a new grinding machine which is adapted for easily and automatically detecting the tangency conditions of the grinding wheel with its environment, in particular with a shaping tool and a chuck which belongs to holding means of the grinding machine.

To this end, the invention concerns a grinding machine for bearing rings, this machine including a frame, a rotating grinding wheel movable in rotation around a first rotation axis, a working station where a bearing ring stands during a grinding operation of one of its surfaces, a chuck for holding a bearing ring in the working station, this chuck being movable in rotation along a second rotation axis. According to the invention, the machine also includes:

first automatic means to set the position of a shaping tool with respect to an outer peripheral edge of the grinding wheel, these first automatic means including an electric motor, an encoder coupled to the electric motor to detect a rotation of an output shaft of this motor, a sensor of the position of the shaping tool along a translation axis and means to compare an output signal of the encoder and an output signal of the sensor,

-   -   second automatic means to set the axial position of the chuck         along the second rotation axis, these second automatic means         including an electric motor for driving the chuck in translation         along the second rotation axis and means to detect a rotation of         the chuck around the second rotation axis.

Thanks to the invention, the first and second automatic means can be used one after the other, in any order, to set the tangency conditions between, on the one hand, the outer peripheral edge of the grinding wheel and the shaping tool and, on the other hand, a lateral surface of the grinding wheel and the chuck. In both cases, these settings can be obtained in a fast and reproducible way, since one does not need to rely on a human operator.

The sensor of the first automatic means is advantageously an optical scale sensor. Preferably, the machine includes means for moving the grinding wheel from a position offset with respect to the second rotation axis to a second position where a lateral face of the grinding wheel intersects the second rotation axis.

The invention also relates to a method which can be implemented with a grinding machine as mentioned here-above and, more specifically, a method for setting the tangency conditions between a grinding wheel and its environment in a grinding machine for bearing rings, this machine including, in addition to the grinding wheel which rotates around a first rotation axis, a frame, a working station where a bearing ring stands during a grinding operation of one of its surfaces and a chuck for holding the bearing ring in the working station, this chuck being movable in rotation around a second rotation axis. According to the invention, this method includes at least the following steps consisting in:

-   -   a) moving a shaping tool, to be used for shaping an outer         peripheral edge of the grinding machine, in translation along a         transverse axis, towards the first rotation axis by actuation of         a first electric motor,     -   b) detecting a rotation of an output shaft of the electric motor         via an encoder coupled to the electric motor,     -   c) detecting a position of the shaping tool along the transverse         axis via a dedicated sensor,     -   d) comparing a first output signal of the encoder with a second         output signal of the dedicated sensor,     -   e) assessing that the shaping tool is tangent with the outer         peripheral edge of the grinding wheel when the first output         signal is representative of a rotation of the output shaft and         the second output signal is representative of a stop of the         shaping tool along the transverse axis,     -   f) moving the grinding wheel to a position where a lateral         surface of the grinding wheel intersects the second rotation         axis,     -   g) moving the grinding wheel in rotation around the first         rotation axis,     -   h) moving the chuck in translation along the second rotation         axis, towards the lateral surface of the grinding wheel by         actuation of a second electric motor,     -   i) detecting a rotation of the shaft integral in rotation with         the chuck via a dedicated rotation sensor,     -   j) assessing that the chuck is tangent with the lateral surface         of the grinding wheel as soon as the dedicated rotation sensor         detects a rotation of the shaft.

Steps a) to e) can be performed before or after steps f) to j).

According to further aspects of the invention which are advantageous but not compulsory, one can provide that:

-   -   when it is assessed in step e) that the shaping tool is tangent         with the outer peripheral edge of the grinding wheel, the first         electric motor is stopped, and/or     -   when it is assessed in step j) that the chuck is tangent with         the lateral surface of the grinding wheel, the second electric         motor is stopped.

Moreover, this invention also concerns methods for shaping an outer peripheral edge of a grinding wheel or an axial surface of a chuck of a grinding machine as mentioned hereabove, wherein one implements a method as mentioned here-above.

For shaping of an outer peripheral edge of a grinding wheel, one uses an extra step k), implemented after step e), when it assessed that the shaping tool is tangent with the peripheral edge, and consisting in j) moving the shaping tool in translation along the transverse axis, towards the first rotation axis, over a given stroke.

For shaping an axial surface of the chuck, one uses the following step l), implemented after step j), when it is assessed that the chuck is tangent with the lateral surface of the grinding wheel, and consisting in moving the chuck in translation along the second rotation axis, towards the grinding wheel, over a given stroke.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on the basis of the following description which is given in correspondence with the annexed figures and as an illustrative example, without restricting the object of the invention. In the annexed figures:

FIG. 1 is a front view of a grinding machine according to the invention;

FIG. 2 is a partial perspective view corresponding to detail II on FIG. 1;

FIG. 3 is a top schematic view of a portion of the grinding machine of FIGS. 1 and 2 where only some elements of the machine are represented; and

FIG. 4 is a top schematic view similar to FIG. 3 when the grinding machine is in another configuration.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The grinding machine 2 represented on FIGS. 1 to 4 includes a frame 4 and a rotating grinding wheel 6 which rotates around a first rotation axis X6. An electric motor 8 is used to drive wheel 6 in rotation around axis X6. D6 denotes the outer diameter of grinding wheel 6.

Grinding wheel 6 and motor 8 are supported by an auxiliary frame 9 which is movable with respect to frame 4 in two opposite directions perpendicular to axis X6, as shown by double arrow A9 on FIG. 1. Axis X6 is fixed with respect to auxiliary frame 9.

The outer peripheral surface 10 of grinding wheel 6 is shaped by a knurl 12 when needed and is used to grind the outer surface of an inner ring 500 of a non-further represented bearing. Knurl 12, which is sometimes called “diamant roller”, is also supported by auxiliary frame 9. In the example of the figures, outer surface 10 has a central bump 110, so that it is used to grind the outer radial surface 502 of ring 500 with a concave groove 502A.

Grinding machine 2 is provided with a working station or zone 14 where each ring 500 is successively held in position with respect to grinding wheel 6 during a grinding operation.

Working station 14 includes two support shoes 16 and 18, each provided with a fitting 20, respectively 22. Fitting 20 is adapted to lie against the outer radial surface of a magnetic clamp 24, whereas fitting 22 is made of two parts and adapted to lie against the outer peripheral surface 502 of ring 500. Each support shoe 16 and 18 is mounted on a slider 26, respectively 28. Another slider 30 is used to avoid escape of the ring 500.

When it is loaded in working station 14, as shown on FIGS. 1, 2, and 3, each ring 500 is centered around a central axis X24 of magnetic clamp 24 parallel or substantially parallel to axis X6. In this configuration, the central bore 504 of ring 500 is empty and, because of the friction between surfaces 10 and 502, ring 500 is driven in rotation around axis X24 by the rotation movement of grinding wheel 6 around axis X6. Ring 500 is cut on FIG. 3, in order to show central bore 504.

Two types of equipment are used to feed working station 14 with rings 500 and to evacuate the rings from this working station, once they have been processed. In this description, a ring which is not yet processed is called a “black ring”, whereas a ring which has been processed by grinding wheel 6 is called a “ground ring”.

A multi-axis robot 100, with 6 degrees of freedom, belongs to the transfer means. It is mounted by its base 102 on the frame 4 of grinding machine 2 and includes a multi-articulated arm 104 whose free end is equipped with a clamp 106 adapted to grasp or grip different types of rings 500, via a proper programming of robot 100.

A moving arm 200 also belongs to the transfer means. This moving arm 200 is rotatable around an axis X200 which is fixed with respect to frame 4 and parallel to axis X6. Near its free end 204 opposite to axis X200 moving arm 200 is provided with means for gripping a ring 500 to be moved away from working station 14.

Grinding machine 2 includes an inlet chute 300 where black rings 500 move by gravity in the direction of arrow A300. For the sake of simplicity, only one ring 500 is represented in inlet chute 300 on FIG. 2. Inlet chute 300 is close to robot 100 which can pick-up a ring 500 present in inlet chute 300 when needed.

On the other hand, grinding machine 2 also includes an outlet chute 310 where ground rings 500 are dumped, one after the other. In outlet chute 310, ground rings 500 move by gravity, in the direction of arrow A310. On its side oriented towards arm 200, outlet chute 310 is equipped with a releaser 312 provided with a notch 314 of a size sufficient to accommodate the gripping means of moving arm 200 but with a transverse dimension, measured between two lateral edges of this notch, smaller than the outer diameter of the rings 500.

Knurl 12 is movable with respect to axis X6 along an axis Y12 which is radial with respect to axis X6. Such a movement is necessary in order for knurl 12 to be in contact with the outer peripheral surface or edge 10 of ring 6 when it is necessary to conform this edge 10 with a new shape, to be used for a new type of bearing ring 500 to be processed on machine 2. The movements of knurl 12 along axis Y12 are driven by an electric motor 702 whose output shaft 704 primes a ball screw mechanism 706 having an output slide rigidly connected to knurl 12. Thus, depending on the electric current feeding motor 702, it is possible to move knurl in translation along axis Y12, in the directions of double arrow A12.

An optical scale sensor 708 is arranged between ball screw mechanism 706 and knurl 12. It includes a fixed graduation 708A and a slide 708B which moves along graduation 708A and includes a sensing unit 708C capable of reading graduations 708A. Slide 708B is rigidly connected to knurl 12. Thus, optical scale sensor 708 is capable of delivering to an electronic control unit or ECU 800 a signal 5708 representative of the actual position of knurl 12 along axis Y12.

In other words, knurl 12 itself is used as the “feeler” or “probe” of optical scale 708.

On the other hand, an encoder 710 is coupled to electric motor 702 and capable of delivering to ECU 800 an electric signal 5710 representative of the angular position or speed of the non represented rotor of electric motor 702 that is of output shaft 704.

When it is needed to use knurl 12 in order to set a new shape on outer peripheral surface or edge 10 of grinding wheel 6, electric motor 702 is actuated in order to move knurl 12 towards axis X6 along axis Y12. During this movement and at regular time slots, e.g. every 100 ms, optical scale sensor 708 and encoder 710 provide ECU 800 with their respective output signals 5708 and 5710.

When knurl 12 becomes tangent to outer peripheral surface 10, slide 708B is blocked along graduation 708A and signal 5708 is representative of a stop of slide 708B. On the other hand, at the same moment, encoder 710 still detects that output shaft 704 rotates because the rotation of ball screw mechanism 706 has not yet been blocked by the reaction of knurl 12. Thus, the output signal 5710 of encoder 710 is representative of a rotation of output shaft 704.

ECU 800 includes a microcontroller which is programmed to assess that, when signal S708 is representative of a stop of slide 708B and when signal 5710 is representative of a rotation of output shaft 704, a tangency point has been reached, along axis Y12, between knurl 12 and outer peripheral edge 10.

Then, a control signal 5702 is sent to motor 702 in order to stop it, in case it has not already been stopped by a torque limitation module or any equivalent equipment.

Once a tangency condition has been detected between knurl 12 and outer peripheral surface or edge 10 of grinding wheel 6, it is possible to implement with knurl 10 a shaping operation of edge 10 in predetermined conditions, in particular by machining edge 10 over a given depth along axis Y12. The fact that the tangency condition is determined prior to starting this machining operation guarantees that the machining operation is fully implemented, with a minimum decrease of the diameter of grinding wheel 6, since machining of edge 10 occurs on a given stroke which is optimized.

The use of optical scale sensor 708 as a dedicated sensor of the position of knurl 12 along axis Y12 is very convenient since such a sensor is reliable, simple to implement and economical. However, other types of sensors can be used, such as a magnetostrictive sensor. However an optical scale sensor is by far preferred because of its high resolution capability, with an order of magnitude of one micrometer.

Magnetic clamp 24 includes a solenoid activated clutch 242 and a chuck 244 made of a magnetic material, such as iron, which has a front annular face 244A adapted to come into contact with a back axial surface 506A of a bearing ring 500 present in working station 14. Back axial surface 506A is opposite to a front axial surface 506B of this ring which is visible from outside machine 2 in the direction of FIG. 1.

A shaft 246 also belongs to magnetic clamp 24 and connects clutch 242 and chuck 244.

It is essential that annular surface 244A is correctly shaped in order to efficiently transfer a magnetic effort to a ring 500 present in working station 14, via a surface/surface contact with axial surface 506A of this ring. Such a correct geometry of surface 244A can be obtained through a grinding operation of this surface via grinding wheel 6. The success of such a grinding operation depends, amongst others, from its starting point where surface 244A should be tangent with a lateral surface 62 of grinding wheel 6.

In order to obtain such a tangency configuration, one uses an electric motor 902 to drive magnetic clamp 24 in translation axially along axis X24. The output shaft 904 of electric motor 902 is connected to a ball screw mechanism 906 which transforms the rotational movement of output shaft 904 into a bidirectional translational movement as represented by arrow A24 and A′24 on FIGS. 3 and 4.

An encoder 910, coupled to magnetic clamp 24 and capable of detecting a rotation of shaft 246 around axis X24, delivers to ECU 800 a signal 5910 representative of the rotation of shaft 246.

On the other hand, ECU 800 is capable of piloting electric motor 902 with an appropriate signal 5902.

When it is needed to re-shape or re-conform annular surface 244A, ECU 800 controls electric motor 902 in order to move magnetic clamp backwards with respect to grinding wheel 6, which is in the direction of arrow A24 in FIG. 3, whereas no ring 500 is mounted on chuck 244.

Then, auxiliary frame 9 is moved towards axis X24, in the direction of arrow A′9 on FIG. 4. This brings grinding wheel 6 in front of magnetic clamp 24. In other words, the movement of auxiliary frame 9 in the direction of arrow A′9 induces that lateral surface 62 of grinding wheel 6 crosses axis X24.

This movement can also be controlled via ECU 800, via a non represented electric motor.

ECU 800 also controls electric motor 8 in order to drive grinding wheel 6 in rotation around axis X6. Driving in rotation of grinding wheel 6 can start before or after the end of the translation movement of auxiliary frame in the direction of arrow A′9.

Thereafter, ECU 800 controls electric motor 902 in order for it to move magnetic clamp towards grinding wheel 6, in the direction of arrow A′24 on FIG. 4. The consequence is that annular surface 244A of chuck 244 comes into contact with lateral surface 62 of grinding wheel 6. The time moment when this occurs is detected via encoder 910 since, as soon as a contact exists between surfaces 244A and 62, chuck 244 is driven in rotation around axis X24, which also drives in rotation shaft 246 whose rotation is detected by encoder 910. Thus, as soon as surface 244A comes tangent to surface 62, ECU 800 is informed via signal 5910 which is representative of the beginning of a rotational movement of shaft 246 around axis X24. As soon as it receives such a signal 5910, ECU 800 stops electric motor 902 via signal 5902.

One is then in the configuration represented on FIG. 4.

Starting from this configuration, ECU 800 actuates electric motor 902 via signal 5902 in order to move magnetic clamp 24, including chuck 244, in the direction of arrow A′24, that is towards grinding wheel 6, on a given straw, between 0.01 and 10 mm, preferably about 0.1 mm. This induces that surface 244A is ground by lateral surface 62 of grinding wheel 6, on a predetermined depth, so that surface 244A becomes fully effective to cooperate with surface 506A of a bearing ring presenting working station 14. 

1. A grinding machine for bearing rings, the grinding machine including: a frame; a rotating grinding wheel movable in rotation around a first rotation axis; a working station where a bearing ring stands during a grinding operation of one of its surfaces; a chuck for holding a bearing ring in the working station, this chuck being movable in rotation around a second rotation axis; a first automatic mechanism to set a position of a shaping tool with respect to an outer peripheral edge of the grinding wheel, the first automatic mechanism includes an electric motor, an encoder coupled to the electric motor to detect a rotation of an output shaft of the motor, a sensor of the position of the shaping tool along a translation axis and a comparator to compare an output signal of the encoder and an output signal of the sensor; and a second automatic mechanism to set the axial position of the chuck along the second rotation axis, these second automatic mechanism including an electric motor for driving the chuck in translation along the second rotation axis and a sensor to detect a rotation of the chuck around the second rotation axis.
 2. The machine according to claim 1, wherein the sensor of the first automatic mechanism is an optical scale sensor.
 3. The machine according to claim 1, further comprising a movement mechanism for moving the grinding wheel from a first position offset with respect to the second rotation axis to a second position where a lateral face of the grinding wheel intersects the second rotation axis.
 4. A method for setting the tangency conditions between a grinding wheel and its environment in a grinding machine for bearing rings, the machine including: in addition to the grinding wheel which rotates around a first rotation axis; a frame; a working station where a bearing ring stands during a grinding operation of one of its surfaces; a chuck for holding a bearing ring in the working station, this chuck being movable in rotation along a second rotation axis; the method comprising steps of: a) moving a shaping tool, to be used for shaping an outer peripheral edge of the grinding machine, in translation along a transverse axis, towards the first rotation axis by actuation of a first electric motor, b) detecting a rotation of an output shaft of the electric motor via an encoder coupled to the electric motor, c) detecting a position of the shaping tool along the transverse axis via a dedicated sensor, d) comparing a first output signal of the encoder with a second output signal of the dedicated sensor, e) assessing that the shaping tool is tangent with the outer peripheral edge of the grinding wheel when the first output signal is representative of a rotation of the output shaft and the second output signal is representative of a stop of the shaping tool along the transverse axis, f) moving the grinding wheel to a position where a lateral surface of the grinding wheel intersects the second rotation axis, g) moving the grinding wheel in rotation around the first rotation axis, h) moving the chuck in translation along the second rotation axis, towards the lateral surface of the grinding wheel, by actuation of a second electric motor, i) detecting a rotation of a shaft integral in rotation with the chuck via a dedicated rotation sensor, and j) assessing that the chuck is tangent with the lateral surface of the grinding wheel as soon as the dedicated rotation sensor detects a rotation of the shaft.
 5. The method according to claim 4, wherein when assessed in step e) that the shaping tool is tangent with the outer peripheral edge of the grinding wheel, the first electric motor is stopped.
 6. The method according to claim 4, wherein when assessed in step j) that the clutch is tangent with the lateral surface of the grinding wheel, the second electric motor is stopped.
 7. A method for shaping an outer peripheral edge of a grinding wheel of a grinding machine, the grinding machine comprising: a frame; a rotating grinding wheel movable in rotation around a first rotation axis; a working station where a bearing ring stands during a grinding operation of one of its surfaces; a chuck for holding a bearing ring in the working station, this chuck being movable in rotation around a second rotation axis; a first automatic mechanism to set a position of a shaping tool with respect to an outer peripheral edge of the grinding wheel, the first automatic mechanism includes an electric motor, an encoder coupled to the electric motor to detect a rotation of an output shaft of the motor, a sensor of the position of the shaping tool along a translation axis and a comparator to compare an output signal of the encoder and an output signal of the sensor, a second automatic mechanism to set the axial position of the chuck along the second rotation axis, these second automatic mechanism including an electric motor for driving the chuck in translation along the second rotation axis and a sensor to detect a rotation of the chuck around the second rotation axis; the method comprising steps of: a) moving a shaping tool, to be used for shaping an outer peripheral edge of the grinding machine, in translation along a transverse axis, towards the first rotation axis by actuation of a first electric motor, b) detecting a rotation of an output shaft of the electric motor via an encoder coupled to the electric motor, c) detecting a position of the shaping tool along the transverse axis via a dedicated sensor, d) comparing a first output signal of the encoder with a second output signal of the dedicated sensor, e) assessing that the shaping tool is tangent with the outer peripheral edge of the grinding wheel when the first output signal is representative of a rotation of the output shaft and the second output signal is representative of a stop of the shaping tool along the transverse axis, f) moving the grinding wheel to a position where a lateral surface of the grinding wheel intersects the second rotation axis, g) moving the grinding wheel in rotation around the first rotation axis, h) moving the chuck in translation along the second rotation axis, towards the lateral surface of the grinding wheel, by actuation of a second electric motor, i) detecting a rotation of a shaft integral in rotation with the chuck via a dedicated rotation sensor, and j) assessing that the chuck is tangent with the lateral surface of the grinding wheel as soon as the dedicated rotation sensor detects a rotation of the shaft. k) moving the shaping tool in translation along the transverse axis, towards the first rotation axis, over a given stroke, wherein step k is implemented after at least one of: step e) when it is assessed that the shaping tool is tangent with the outer peripheral edge, and step j) when it is assessed that the chuck is tangent with the lateral surface of the grinding wheel. 